Valuable clinical and physiological data concerning blood and tissue oxygenation can be obtained from continuous transcutaneous monitoring of both hemoglobin oxygen saturation (SaO2) and oxygen tension (PO2) in arterial blood. While periodic blood sampling is still used clinically to determine arterial blood gases, it is becoming apparent that the recent introduction of continuous noninvasive monitoring of blood gases can offer many advantages. A noninvasive method is superior to direct blood measurements if it is accurate. Since transcutaneous PO2 is a good indicator of tissue hypoxia and transcutaneous SaO2 is a direct measure of aterial hypoxemia, a combined SaO2/PO2 sensor which will measure both parameters simultaneously can provide additional information on the status of tissue and blood oxygenation. The combined sensor would have broader medical applications, especially for use in adults where the transcutaneous PO2 often is not reliably related to blood PO2. Thus, the overall objective of this proposal is the research and development of a new noninvasive, combined sensor for monitoring SaO2 and PO2 simultaneously. The specific goal of this bioengineering project is to evaluate the performance of this combined sensor for various physiological conditions. We have successfully built a prototype combined sensor using a standard transcutaneous oxygen tension (Clark type) sensor and a solid state opto-electronic (reflection type) sensor for measuring SaO2. Our pilot studies using this sensor on human volunteers showed that we could simultaneously measure quantitative changes in SaO2 and PO2 from various locations on the body. In these preliminary studies, we observed that variations in blood flow effects transcutaneous PO2 while the SaO2 is significantly less dependent on blood flow. Based upon our pilot studies, we feel that it is important to carefully investigate the implication of monitoring both transcutaneous SaO2 and PO2 under various physiological conditions which may influence these measurements. In vivo animal experiments will be conducted to study the effect of various physiological conditions on the reading from the combined sensor. From this it will be posible to determine which parameter is more important to monitor under various physiological conditions. Furthermore, we will investigate the optimal sensor configuration that would enable us to measure SaO2/PO2 reliably. These preliminary studies will lead to more extensive clinical investigations with the University of Massachusetts Medical School Department of Anesthesia.